1. Field of the Invention
The invention relates to an additive-agent diffusion plate that diffuses an additive agent injected into an exhaust passage for an engine, at a position upstream of an exhaust gas purification device disposed in the exhaust passage, a structure of the additive-agent diffusion plate, and an exhaust system including the additive-agent diffusion plate.
2. Description of the Related Art
Exhaust gas discharged from an engine, particularly, a diesel engine, generally contains pollutants generated by combustion, for example, nitrogen oxides (hereinafter, referred to as NOx) such as nitrogen monoxide. To prevent air pollution, it is strongly required to reduce the amount of such pollutants discharged from the diesel engine. NOx may be discharged, together with exhaust gas, from a direct injection gasoline engine in which gasoline is injected directly into a combustion chamber, depending on an operating condition. Therefore, it is also required to reduce the amount of the pollutants discharged from the direct injection gasoline engine.
Thus, an exhaust gas purification device that includes a three-way catalyst is provided in an exhaust passage, to purify NOx discharged together with the exhaust gas.
However, the exhaust gas purification device including the three-way catalyst may not sufficiently purify NOx, depending on the type of the engine. For example, when employing a lean-burn diesel engine, the exhaust gas contains excessive oxygen, and therefore, a fuel component (HC) easily reacts with the oxygen (i.e., the fuel component (HC) is easily combusted). Thus, it is difficult for the three-way catalyst to sufficiently purify NOx.
Accordingly, for example, Japanese Utility Model Application Publication No. 3-68516 (JP-U-03-68516) describes a technology in which an exhaust gas purification device including a zeolitic catalyst is provided in an exhaust passage, and a fuel component (HC component) is supplied to exhaust gas, at a position upstream of the exhaust gas purification device, to efficiently purify NOx.
Also, for example, Japanese Patent Application Publication No. 2005-113688 (JP-A-2005-113688) describes a technology in which an exhaust gas purification device including a selective reduction NOx catalyst is provided in an exhaust passage, and urea is supplied to exhaust gas, at a position upstream of the exhaust gas purification device, to efficiently purify NOx in the exhaust gas.
The additive agent, such as the fuel component or the urea, needs to be efficiently diffused in the exhaust gas, to increase NOx purification performance of the exhaust gas purification device.
Thus, for example, Japanese Patent Application Publication No. 10-165769 (JP-A-10-165769) describes a technology in which a rectifying lattice, which includes a gas mixing promoter that promotes mixing of exhaust gas and an additive agent (a fuel component or a urea aqueous solution), is provided in an exhaust passage, at a position between a position from which the additive agent is supplied, and an exhaust gas purification device. The rectifying lattice stands in a direction substantially perpendicular to a direction in which the exhaust gas flows, and occupies an entire cross section of the exhaust passage. Thus, the rectifying lattice efficiently diffuses the additive agent in the exhaust gas.
In the technology described in the above-described publication, the gas mixing promoter is provided in at least one section of the additive-agent diffusion plate such as the rectifying lattice. Therefore, if the additive-agent diffusion plate is mounted in the exhaust passage in a manner such that the additive-agent diffusion plate is displaced in a circumferential direction, the gas mixing promoter may be displaced from the intended section. In this case, the additive agent cannot be efficiently diffused.
Further, the additive-agent diffusion plate is formed by combining partition plates in a vertical direction and a horizontal direction. In addition, the gas mixing promoter is constituted by a gas swirl generator that protrudes to face the flow of the exhaust gas, and a gas agitator that is bent in an inverted V-shape to face the flow of the exhaust gas. Therefore, the additive-agent diffusion plate has an extremely complicated structure.